Tennessee Cauliflower & Onion Casserole: A London-Inspired Twist

When I first saw the viral Tennessee Onion Casserole from the New York Times, I was mesmerized.

Layers of caramelized onions, brown sugar, and melted cheese - I was intrigued. "Who eats cheese and onions?" I thought to myself.

But of course, being an adventurous home-chef, I wanted to try it. My curiosity had gotten the best of me.

During my trip to London last year, I discovered the British tradition of cauliflower cheese as a Sunday roast side dish.

They way I gathered (without much research, mind you) cauliflower cheese is like the British version of American macaroni and cheese, the hero to every indulgent meal.

That said, I knew I had to create an elevated, fusion version that honored both the US and the UK and fit in perfectly with my first Sunday Roast.

This casserole takes the best of both worlds: the sweet, caramelized onions and brown sugar from the Tennessee casserole, combined with roasted cauliflower and a rich, creamy cheese sauce inspired by British cauliflower cheese.

It's elevated comfort food that works beautifully as an alternative (or addition) to mac and cheese for your holiday table or Sunday roast.

The Inspiration

The Tennessee Onion Casserole has become a cult favorite for good reason - it's ridiculously simple yet incredibly flavorful.

When I was thinking about what to make for my first Sunday roast at home, my mind kept coming back to all the cauliflower dishes I'd seen in London.

I thought: why not bring these two traditions together? The result is this gorgeous casserole that's rich, savory-sweet, and absolutely perfect alongside roasted chicken, crispy potatoes, and Yorkshire puddings.

Prep Time: 20 minutes

Cook Time: 50-55 minutes

Total Time: 1 hour 15 minutes

Serves: 8-10

Ingredients

For the Vegetables

• 2 large head cauliflower, cut into florets

• 3 medium onions (1 sweet onion + 1 yellow onions work perfectly)

• 1/4 cup olive oil

• 1/2 - 2 tablespoons brown sugar (depending on your palate)

• 1 teaspoon kosher salt

• 1 tablespoon black pepper

• 1 tablespoon paprika

• 1 teaspoon fresh thyme leaves

  
  

For the Cheese Sauce

• 3 tablespoons butter

• 3 tablespoons all-purpose flour

• 1 1/2 cups whole milk

• 1/4 cup heavy cream

• 1 cup shredded sharp cheddar cheese

• 1/2 cup shredded gruyere cheese

• 1/4 cup grated parmesan cheese

• 1/4 cup shredded swiss cheese

• 1/4 cup creme fraiche (optional. If you skip this, then use 1/2 cup heavy cream)

• 1 teaspoon garlic powder

• 1/4 teaspoon nutmeg (optional, but traditional for cheese sauce)

• Salt and pepper to taste

  
  

For the Topping

• 1/2 cup shredded sharp cheddar

• 1/4 cup grated parmesan

• Fresh parsley, chopped (for garnish)

  
  

Instructions

Step 1: Prep and Roast the Vegetables

Preheat your oven to 400°F (200°C).

In a small bowl, combine olive oil, brown sugar, salt, pepper, and thyme

Cut the cauliflower into bite-sized florets.

In a large bowl, toss the cauliflower with 1/2 of the olive oil, brown sugar, salt, pepper, and thyme mixture until everything is well coated.

The brown sugar might seem weird, but trust me - it helps with caramelization and adds a subtle sweetness that balances all the savory flavors.

Spread the cauliflower on a large baking sheet in a single layer (use two sheets if needed - don't crowd them).

Roast for 25-30 minutes, stirring halfway through, until the cauliflower is tender and golden. Remove from oven and reduce temperature to 375°F (190°C).

While cauliflower is roasting, slice the onions into 1/4-inch thick rounds (they'll separate into rings - that's perfect).

In a Dutch over or pot, add sliced onions into the pot and cover with the other 1/2 of the olive oil, brown sugar, salt, pepper, and thyme mixture. Make sure onions are well coated. Stir on medium heat until the onions are soft and caramelized.

Step 2: Make the Cheese Sauce

While the vegetables are roasting and caramelizing, make your cheese sauce.

In a medium saucepan, melt the butter over medium heat. Add the flour and whisk constantly for about 1-2 minutes - you're making a roux. It should smell slightly nutty but not brown.

Gradually whisk in the milk and heavy cream. Keep whisking to avoid lumps.

Bring to a gentle simmer and cook for 3-4 minutes until the sauce thickens enough to coat the back of a spoon.

Reduce heat to low. Add the cheddar, gruyere, parmesan, and Swiss cheese, stirring until everything melts into a smooth, creamy sauce.

Stir in the garlic powder and nutmeg if using. Taste and season with salt and pepper - remember, you'll be adding more cheese on top, so don't oversalt.

Step 3: Assemble the Casserole

Butter a 9x13-inch baking dish generously.

Add the roasted cauliflower and onions to the cheese sauce and fold everything together gently until the vegetables are coated. Pour the mixture into your prepared baking dish and spread it evenly.

Sprinkle the remaining cheddar and parmesan over the top. This cheese layer will get gorgeously golden and crispy in the oven.

Step 4: Bake to Golden Perfection

Bake at 375°F for 20-25 minutes until the top is golden brown and bubbly.

If you want an extra crispy top, hit it with the broiler for 2-3 minutes at the end (watch it closely so it doesn't burn!).

Let it rest for 5-10 minutes before serving. Garnish with fresh chopped parsley and a little more fresh thyme if you'd like.

Tips from Rue's Kitchen

Don't Skip the Brown Sugar: I know it seems unusual, but it's traditional in the Tennessee version and it works beautifully here. It enhances the natural sweetness of the onions and cauliflower without making it taste sweet.

Onion Mix: Using a combination of sweet and yellow onions gives you complexity - the sweet onion adds depth while the yellow onions provide that classic sharp onion flavor.

Cheese Sauce Consistency: You want it thick enough to coat the vegetables but loose enough that it stays creamy when baked. If it's too thick, add a splash more milk. Too thin? Let it simmer a bit longer.

Make It Ahead: You can roast the vegetables and make the cheese sauce up to a day ahead. Store separately in the fridge, then assemble and bake when ready. Add 5-10 minutes to the baking time if assembling from cold.

Seasoning Note: As an American cook, I love bold flavors! I use more salt, pepper, and herbs than the traditional British cauliflower cheese. Feel free to adjust to your preference, but don't be shy - this dish can handle it.

The British Connection

In Britain, cauliflower cheese is a beloved side dish, especially with Sunday roast.

It's comfort food at its finest - tender cauliflower blanketed in a rich cheese sauce. It's that creamy, indulgent side dish that everyone looks forward to.

By adding the Tennessee onion element with its caramelized sweetness and simplicity, I've created something that bridges both traditions.

It's a little bit Southern, a little bit British, and a whole lot of deliciousness.

Serving Suggestions

This casserole is perfect alongside:

• Buttermilk Brined Roasted Chicken

• Crispy Roasted Potatoes

• Yorkshire Puddings

• White Wine Pan Gravy - THIS IS ESSENTIAL

• Caramelized Roasted Root Vegetables

• Green Beans

As part of a complete Sunday Roast

It also makes an excellent holiday side dish - think Thanksgiving, Christmas, or Easter. It's fancy enough to impress but easy enough that you won't stress about it.

Variations

Extra Veggies: Add some roasted garlic cloves to the vegetable mix for even more depth.

Spicy Kick: Add a pinch of cayenne pepper to the cheese sauce or sprinkle red pepper flakes on top.

Herb it Up: Try adding fresh rosemary or sage along with the thyme.

Crispy Topping: If you want extra texture, mix some panko breadcrumbs with melted butter and sprinkle on top for the last 10 minutes of baking.

Storage & Reheating

Storage: Keep leftovers in an airtight container in the fridge for up to 4 days.

Reheating: Reheat in a 350°F oven covered with foil for about 20 minutes, then uncover for the last 5 minutes to re-crisp the top. You can also microwave individual portions, though the top won't be as crispy.

Freezing: This freezes well! Assemble but don't bake, cover tightly, and freeze for up to 2 months. Thaw overnight in the fridge and bake as directed, adding 10-15 minutes to the baking time.

Why This Recipe Works for Sunday Roast

One of the things I love most about Sunday roast is how it brings together so many different flavors and textures on one plate.

You've got your protein, your potatoes, your gravy, your vegetables - and this casserole fits right in.

It's creamy and rich, which balances the crispy potatoes. It's got sweetness from the onions and brown sugar, which complements the savory gravy. And the cauliflower adds that vegetable element in a way that feels indulgent rather than virtuous.

Plus, it's a conversation starter! When people ask what's in it, you get to share the story of how you combined a viral American recipe with a British Sunday roast classic.

Because that's what Rue's Global Kitchen is all about - bringing the best of my travels to your table.

Have you tried the Tennessee Onion Casserole? Or British cauliflower cheese?

Would you try this?

Let me know in the comments which tradition you're more familiar with!

For more fusion recipes inspired by my travels, check out my Sunday Roast and subscribe to Rue's Global Kitchen for weekly recipes and travel stories!